In part, the quality of audio that is played back to a listener depends on how the audio was recorded and how the audio was compressed/decompressed (if at all). A playback device can sometimes perform processing during playback, however, to improve the listening experience.
Bass boost is often desirable for music playback for a number of reasons. For example, bass boost can compensate for limitations of the playback system (e.g., small speakers can sound hollow without adequate bass). Bass boost can make bass audible when a recording mixed for listening in quiet environments is played in noisy environments. Bass boost can satisfy listener taste for boost level, which may differ substantially from the mixing engineer's. Finally, bass boost can compensate for bass level in modern recordings, which in some situations is limited in order to maximize loudness (e.g., since the human ear is less sensitive to bass than midrange/treble, bass does not contribute significantly to loudness and thus optimizing loudness means devoting most of the available signal range to midrange/treble).
In some situations, a fixed (static) bass boost (e.g., a linear filter) sounds good but leads to some problems. For example, in a fixed bass boost filter the desired amount of boost depends on the bass level in the original content, so the user must often adjust the bass control from one piece of content to the next. Furthermore, excessive boost of content that has a lot of bass to begin with tends to produce distortion in analog components of the playback chain (e.g., speakers, headphones, amplifiers). Finally, boosting bass frequencies of a digital representation of a signal runs into digital fullscale saturation problems with most modern content (because the content fully utilizes the available digital range to begin with), which necessitates compromises such as reduction on the overall volume in response to excessive bass levels.
Compression of bass frequencies can also be a desirable effect either separately or in combination with bass boost. Compression of the bass band is an audio effect commonly used in broadcast radio and other situations. The direct approach to bass band compression involves splitting the signal into sub-bands and applying compression separately to the low-frequency sub-band. However, finite precision filter implementation challenges can make it difficult to achieve the desired frequency response for the lower sub-band directly.
Therefore, there exists ample opportunity for improvement in technologies related to boosting bass frequencies of audio.